1. Field of the invention
This invention relates to spark ignitors and more particularly to spark ignitors for liquid propellant guns.
2. Description of the Prior Art
A liquid propellant gun (LPG) is one in which a liquid propellant is burned in a firing chamber to propel a projectile from the gun. Such a gun uses a simpler projectile feed, has a flatter combustion chamber time-pressure characteristic, and more flexible installation and rapid fire features than a conventional gun. The liquid propellant, which may be either a monopropellant, or a fuel and an oxidizer, bipropellant is injected into the bore of the chamber, which is defined on one end by the base of the projectile and on the other by a bolt which a flattened end, termed the bolt nose. The bolt slides forward to seal the injection ports and position the projectile. To fire the LPG, the propellant is ignited by a pyrotechnic, thermal or electrical ignitor.
Previous electrical ignitors employed a center electrode which was free standing and projected into a small precombustion chamber to facilitate propellant ignition. These ignitors are subject to the bending of the center electrode due to pressure in the gun chamber, on the order of 60 Kpsi (411,700 Pa). Prior art ignitors also develop very high electrode temperatures and require frequent replacement. Test results have shown that prior art ignitors are also dependent on electrical polarity.